Jet Quenching at RHIC and LHC

Transcription

1 Jet Quenching at RHIC and LHC Oliver Busch University of sukuba Heidelberg University 1

2 Nuclear modification factor Event plane dependence Semi-inclusive jet-hadron yields Jet shapes, subjets, jet mass Identified jet fragmentation 2

3 Nuclear modification factor Event plane dependence Semi-inclusive jet-hadron yields Jet shapes, subjets, jet mass Identified jet fragmentation selection strongly biased towards: light flavour jet results LHC ALICE 3

4 Hadron nuclear modification factor high-p hadron suppression both at RHIC and LHC hadron observable biased towards leading fragment study the effect for fully reconstructed jets theory: energy loss leading hadron fragmentation parton shower energy loss hadronisation PHENIX, Nucl Part. Phys 38 (2011) CMS, JHEP 04 (2017) 039 4

5 Underlying event jet reconstruction in heavy-ion collisions : difficult due to the high underlying event background not related to hard scattering correct spectra for background fluctuations and detector effects not possible down to lowest jet p fake jets central jet area ~ 0.5 (R = 0.4) peripheral 5

6 Experimental aspects / differences jet reconstruction: EM + hadron calorimeter based (ALAS) charged track + EMCal based (SAR + ALICE) particle flow (CMS) fake jet rejection: constituent p cuts leading constituent bias / track jet matching di-jet (hadron-jet) coincidence subtraction. consistently applied to the reference, but may introduce physics bias background subtraction: median density from clusters (ALICE, SAR) iterative geometrical (ALAS, CMS) corrections: for detector effects (efficiency, resolution) and background fluctuations (resolution-like) typical: full corrections to particle level sometimes: detector and/or background effects applied to a reference 6

7 complementarity of LHC experiments ALICE: charged jets from charged particle tracking + full jets from tracking + em. Calorimeter ALAS/CMS: em. + hadronic calorimetry (+tracking) complementary jet p reach, ALICE typically lower constituent p cutoff ALICE, Phys. Lett. B 722 (2013) 262 CMS, PRD 87 (2012)

8 Jet nuclear modification factor: ALAS ALAS jet RAA at snn = 2.76 ev, R = 0.4 strong suppression observed, similar to hadron RAA parton energy not recovered inside jet cone stronger suppression for more central events weak p dependence ALAS, PRL 114, JEWEL and YaJEM jet quenching models reproduce suppression

9 Jet nuclear modification factor: ALICE ALICE full jet RAA at snn = 2.76 ev, R = 0.2 Phys.Lett. B746 (2015) 1 p const,ch > 150 MeV, E Cluster > 300 MeV, p lead, ch > 5 GeV/c maybe hint for weak p dependence JEWEL: PLB 735 (2014) YaJEM:PRC 88 (2013) JEWEL and YaJEM jet quenching models reproduce suppression 9

10 Jet nuclear modification factor: CMS CMS jet RAA at snn = 2.76 ev, R = 0.2, 0.3, 0.4 constituent p > 150 MeV/c, fake jet spectrum from background events subtracted no significant R dependence for p > 70 GeV/c CMS, nucl-ex/

11 Angular dependence R dependence sensitive to broadening of transverse jet profile ALAS RCP double ratio: R dependence seen, in particular for low p and high R not observed in ALICE (but small R difference) ALAS, PLB 719 (2013) 220 ALICE, JHEP 03 (2014)

12 Rapidity dependence expect stronger energy loss for gluons than for quarks ALAS: no significant rapidity dependence of RAA, despite change in q/g balanced by parton spectral slope, y-dependence of energy density? role of fluctuations / biases? ALAS, PRL 114,

13 s depencence ALICE, HP 2016 comparison of different s constrains energy density dependence no significant difference increased energy loss compensated by flatter parton spectrum? ALAS, QM

14 Jet Azimuthal Anisotropy 14

15 Local background subtraction ALICE jet v2: event plane from forward/backward V0 scintillators account for flow-modulation of background via event-by-event fit and subtraction of local background density unfolding to account for background fluctuations : separately for spectra in- and out-of-plane (ϕ) (GeV/c) Pb-Pb s NN Single event = 2.76 ev ALICE ρ ch 100 Phys. Lett. B753 (2016) < p < 5 GeV/c, η < 0.9, track track ρ (ϕ) ch ρ 0 ρ (1+2v cos(2[ϕ-ψ ])) 0 2 EP, 2 ρ (1+2v cos(3[ϕ-ψ ])) 0 3 EP, ϕ (rad) \ 15

16 Charged jet v2: results quantify azimuthal asymmetry via 2 nd Fourier harmonic ch jet v2 central collisions: sigma from v2 ch jet = 0 consistent with 0, but maybe hint for effect of initial density fluctuations? non-zero v2 ch jet in semi-central collisions 0-5% 30-50% {EP, η >0.9 } ch jet v ch jet v 2 0-5%, Stat unc. Syst unc. (shape) Syst (correlated) Syst unc. (correlated) ALICE Pb-Pb s NN = 2.76 ev R = 0.2 anti-k, η <0.7 jet {EP, η >0.9 } ch jet v ch jet v %, Stat unc. Syst unc. (shape) Syst (correlated) Syst unc. (correlated) ALICE Pb-Pb s NN = 2.76 ev R = 0.2 anti-k, η <0.7 jet 0 (a) p > 0.15 GeV/c, p > 3 GeV/c, track, lead ch jet p (GeV/c) Phys. Lett. B753 (2016) (b) p > 0.15 GeV/c, p > 3 GeV/c, track, lead ch jet p (GeV/c) 16

17 Comparison to previous results ALICE + CMS single particles, ALAS full jets : different energy scales! non-zero v2 up to high p CMS, PRL 109 (2012) 022 ALAS, PRL 111 (2013) 152 ALICE, Phys. Lett. B753 (2016) 511 ALICE, Phys. Lett. B719 (2013) 18 jet, v 2 part v ALICE Pb-Pb = 2.76 ev s NN R = 0.2 anti-k, η <0.7 jet ch jet v 2 0-5%, Stat unc. Syst unc. (shape) Syst unc. (correlated) calo jet 5-10% part ALAS v 2 CMS v 2 { η >3} 0-10% part ALICE v 2 { η >2} 0-5% jet, v 2 part v ALICE Pb-Pb = 2.76 ev s NN R = 0.2 anti-k, η <0.7 jet ch jet v %, Stat unc. Syst unc. (shape) Syst unc. (correlated) ALAS v 2 calo jet 30-50% part CMS v 2 { η >3} 30-50% part ALICE v 2 { η >2} 30-50% (a) p > 0.15 GeV/c, p > 3 GeV/c, track, lead part jet p, p (GeV/c) 0 (b) p > 0.15 GeV/c, p > 3 GeV/c, track, lead part jet p, p (GeV/c) 17

18 Comparison to JEWEL good agreement with JEWEL in semi-central collisions clear indication of path-length dependence of energy loss caveat: no transverse expansion in JEWEL ch jet v ch jet v 2 ch jet v 2 0-5%, JEWEL 0-5%, Stat unc. Syst unc. (shape) Syst unc. (correlated) ALICE Pb-Pb s NN = 2.76 ev R = 0.2 anti-k, η <0.7 jet ch jet v ch jet v 2 ch jet v %, JEWEL 30-50%, Stat unc. Syst unc. (shape) Syst unc. (correlated) ALICE Pb-Pb s NN = 2.76 ev R = 0.2 anti-k, η <0.7 jet (a) lead p > 0.15 GeV/c, p, track ch jet p (GeV/c) > 3 GeV/c 0 (b) lead p > 0.15 GeV/c, p, track ch jet p (GeV/c) > 3 GeV/c Phys. Lett. B753 (2016)

19 Semi-Inclusive Hadron-Jet Distributions 19

20 Hadron triggered recoil jets charged jets recoiling from charged hadron hadron biased towards surface Δrecoil: difference between hadron trigger p classes further fake jet removal ALICE, JHEP 09 (2015)

21 ΔIAA Δrecoil divided by PYHIA reference: significant suppression observed subtraction technique allows for large R up to 0.5 with constituent p > GeV/c, no leading constituent bias ALICE, JHEP 09 (2015)

22 ΔIAA: R dependence R dependence as expected for vacuum fragmentation (PYHIA) no medium-induced broadening observed for recoil jets ALICE, JHEP 09 (2015)

23 Medium-induced acoplanarity? Δφ hadron-jet: potentially sensitive to large-angle scattering data compared to embedded PYHIA reference no significant effect within present uncertainties ALICE, JHEP 09 (2015)

24 SAR charged jets, mixed event background subtraction ICP(central-peripheral): jet suppression observed Recoil jets at RHIC estimate E-loss through spectral shift ΔE : energy transported out-of-cone smaller at RHIC than LHC SAR, nucl-ex/

25 Recoil jets at RHIC: R dependence no evidence of broadening SAR, nucl-ex/

26 Intrajet Observables and Subjets 26

27 27 Jet shapes radial moment girth g, longitudinal dispersion pd, difference leading - subleading p LeSub shapes in pp collisions at 7 ev: - constrain QCD calculations of small-r jets ( microjets : M. Dasgupta, F. Dreyer, G. Salam, G. Soyez hep-ph/ ) - validate MC simulations shapes in Pb-Pb probe of quenching of low-p jets: characterise fragment distributions and are sensitive to medium induced changes of intra-jet momentum flow event-by-event measure, sensitive to fluctuations infrared (& collinear) safe

28 28 Jet shapes in Pb-Pb R=0.2, 40 < p jet < 60 GeV/c, no leading constituent cut, fully corrected to charged particle level g shifted to smaller values compared to PYHIA reference indicates more collimated jet core dn/dg jets 1/N ALICE Preliminary Pb-Pb s NN = 2.76 ev Anti-k charged jets, R = < p jet,ch < 60 GeV/c ALICE Data Shape uncertainty Correlated uncertainty PYHIA Perugia ALI PREL g

29 29 larger pd in Pb-Pb compared to PYHIA indicates fewer constituents in quenched jets (or less democratic splitting) LeSub in Pb-Pb in good agreement with Pb-Pb: hardest splittings likely unaffected D dn/dp jets 1/N ALI PREL ALICE Preliminary Pb-Pb Anti-k 40 < p s NN = 2.76 ev charged jets, R = 0.2 jet,ch <60 GeV/c ALICE Data Shape uncertainty Correlated uncertainty PYHIA Perugia p D (c/gev) dn/dlesub jets 1/N ALI PREL ALICE Preliminary Pb-Pb Anti-k 40 < p s NN = 2.76 ev charged jets, R = 0.2 jet,ch < 60 GeV/c ALICE Data Shape uncertainty Correlated uncertainty PYHIA Perugia LeSub (GeV/c)

30 30 Model comparison trends reproduced by JEWEL indicates collimation through emission to large angles recoils off : no medium recoils partons in final state (note R=0.2)

31 declustering and soft drop grooming to identify hard jet substructure subjet momentum balance Subjets at LHC in vacuum, dσ/dzg ~ splitting function CMS: strongest suppression for lower pj jet at high zg CMS PAS HIN

32 select dijet pairs matching to hard core jets reconstructed with high constituent cut p const > 2 GeV/c no suppression observed Subjets in SAR role of different kinematics, SAR selection bias, subjet ΔR cut? SAR, HP

33 ALICE subjets charged jets, kt declustering subjettyness N: how consistent is a jet with having N subjets 2/ 1 : no significant modification ALICE, QM

34 subjet distance ΔR ALICE subjet ΔR data uncorrected for det. effects and background fluctuations compared to PYHIA embedded reference no significant modification observed relative to reference, full correction to particle level in progress ALICE, QM

35 Jet Mass 35

36 36

37 Mass and virtuality invariant mass of jet constituents, related to virtuality of initial parton parton from hard scattering produced off-shell in vacuum: virtuality decreases at each emission in medium, virtuality can rise due to scatterings quenching observable (A. Majumder, J. Putschke, nucl-th ) soft constituents far from jet axis within cone larger mass few hard constituents smaller mass 37

38 Results: Pb-Pb jet Mass in Pb-Pb collisions at snn = 2.76 ev fully corrected for detector effects and background fluctuations via 2D unfolding small s dependence is expected (quark / gluon composition) compare the ratio Pb-Pb / ppb to the ratio in PYHIA at the 2 energies ALICE, nucl-ex /

39 Ratio Pb-Pb / p-pb slope indicates that Pb-Pb distribution is shifted towards smaller masses with respect to ppb overall small modification - cancellations? ALICE, nucl-ex / Oliver Busch HI café, okyo 2017/01 39

40 Model comparison data lies in between PYHIA and JEWEL with recoils off Q-PYHIA and JEWEL with recoils on produce too large mass ALICE, nucl-ex / Q-PYHIA: radiative energy loss modelled by enhanced splitting functions (N. Armesto, L. Cunqueiro, C. A. Salgado, hep-ph/ ) Oliver Busch HI café, okyo 2017/01 40

41 Strangeness Production in Jets 41

42 Charged particle fragmentation ALAS, CMS: enhancement at low z observed for unidentified charged particles in high-p jets p ch > 2 GeV/c (ALAS), 1 GeV/c (CMS) ALAS, PLB 739 (2014)

43 Strangeness production in nuclear collisions Inclusive strangeness production in Pb-Pb: Baryon / Meson ratio enhanced - collective effects? - parton recombination? - jet fragmentation? Phys. Rev. Lett. 111 (2013) measurement of identified particles in jets helps to constrain hadronisation and energy loss scenarios 43

44 Strangeness in jets neutral strange particles reconstructed via decay topology ( V 0 ): V 0 - jet matching signal extraction via invariant mass corrections for efficiency, feed-down, UE background + fluctuations 44

45 (Λ+Λ)/2K 0 s ratio in jets ratio in jets significantly lower than for inclusive hadrons compare Pb-Pb results to reference from p-pb collisions at 5.02 ev: 2 agreement within uncertainties p-pb 0 Λ)/2K (Λ + S ALICE Preliminary Pb-Pb Pb Pb, s NN in jets, p in jets, p = 2.76 ev, 0 10 % jet,ch jet,ch > 10 GeV/c > 20 GeV/c feed-down uncertainty 0 inclusive Λ/K, ALICE, S (0 5 %, y < 0.5) 0 V η 0 < 0.7 V anti-k t, R = 0.2 η < 0.5 jet,ch p track p leading track > 5 GeV/c > 150 MeV/c 0.2 ALI-PREL ALI PREL p (GeV/c) 45

46 Strange particle spectra in jets spectra of K 0 S and Λ particles in jets: more differential observable to increase sensitivity to potentially modified fragmentation K 0 S spectra in jets follow similar slope as predicted by PYHIA simulations Λ shape different? More reliable reference needed! (c/gev) ) dn/dp 2 1/(N jets πr Pb Pb, = 2.76 ev, 0 10 % s NN ALICE Preliminary p jet,ch 0 Ks, stat. unc., (x 1.5) (Λ+Λ)/2, stat. unc. syst. unc. 0 s full markers K, (x 1.5) open markers (Λ+Λ)/2 PYHIA 8 - tune Monash PYHIA 6 - tune Perugia 2011 PYHIA 6 - tune Perugia NoCR p jet smeared with true σ (δp > 10 GeV/c jet ) (c/gev) ) dn/dp 2 1/(N jets πr Pb Pb, = 2.76 ev, 0 10 % s NN ALICE Preliminary p jet,ch 0 Ks, stat. unc., (x 1.5) (Λ+Λ)/2, stat. unc. syst. unc. 0 s full markers K, (x 1.5) open markers (Λ+Λ)/2 PYHIA 8 - tune Monash PYHIA 6 - tune Perugia 2011 PYHIA 6 - tune Perugia NoCR p jet smeared with true σ (δp > 20 GeV/c jet ) ALI PREL η V 0 < 0.7 anti-k t, R = 0.2 η < 0.5 p track p jet,ch leading track > 5 GeV/c > 150 MeV/c p (GeV/c ) ALI PREL η V 0 < 0.7 anti-k t, R = 0.2 η < 0.5 p track p jet,ch leading track > 5 GeV/c > 150 MeV/c p (GeV/c ) 46

47 Summary LHC inclusive jet RAA and recoil jet measurements at RHIC and LHC subjet momentum balance at LHC and RHIC jet shapes jet mass strange particles in jets 47

48 - Backup - 48

49 full jets, pp at 2.76 ev JES uncertainty ~ 3.6% at p jet = 100 GeV/c ALICE jet response Phys. Lett. B 722 (2013) 262 JHEP 03 (2014) 013 charged jets: Pb-Pb JE resolution at low p dominated by background, at high p by detector effects 49

50 Jet Structure : Model Comparison trends reproduced by JEWEL jet quenching model JEWEL: K.C. Zapp, F. Kraus, U.A. Wiedemann, JHEP 1303 (2013)

51 q/g fraction Spousta, Cole, hep-ph/

52 jet mass: ppb jet mass in ppb collisions at snn = 5.02 ev, charged jets with R=0.4 overall well described by PYHIA with some tension in the tails (c 2 /GeV) < p (GeV/c) < 80, ch jet ALICE Preliminary (c 2 /GeV) < p (GeV/c) < 100, ch jet (c 2 /GeV) 100 < p (GeV/c) < 120, ch jet 0.2 p-pb s = 5.02 ev NN dn dm ch jet 1 N jets 0.1 dn dm ch jet 1 N jets 0.1 Anti-k, R = 0.4 dn dm ch jet 1 N jets 0.1 Systematic p-pb PYHIA Perugia (GeV/c 2 ) ALI PREL M ch jet (GeV/c 2 ) M ch jet (GeV/c 2 ) M ch jet Data/PYHIA < p (GeV/c) < 80, ch jet ALICE Preliminary PYHIA Perugia 2011 Data/PYHIA < p (GeV/c) < 100, ch jet p-pb = 5.02 ev s NN Anti-k, R = 0.4 Data/PYHIA < p (GeV/c) < 120, ch jet p-pb / PYHIA(5.02eV) (Sys p-pb) / PYHIA(5.02eV) (GeV/c 2 ) ALI DER M ch jet (GeV/c 2 ) M ch jet (GeV/c 2 ) M ch jet 52

53 Identified hadrons in heavy-ion collisions baryons / meson RAA a probe of gluon / quark energy loss? R AA would expect stronger radiative energy loss for gluons than for quarks - subtle cancellations? - hadron observable biased towards hard fragmentation? Phys. Rev. C 93, ALICE 0-5% Pb-Pb - π + +π + - K +K p + p Charged s NN =2.76 ev study jets to improve our ALI DER understanding of parton energy loss: - PID in reconstructed jets mitigates fragmentation biases - enhanced sensitivity to medium effects measuring soft particles in jets p (GeV/c) note: medium effects likely strongest at scales of ~ medium emperature (J.G. Milhano, K. C. Zapp, hep-ph/ ,. Renk, Phys. Rev. C 81, , B. Mueller, hep-ph/ ) 53

54 generalized angularities 54

55 Underlying event subtraction subtract underlying event contribution to K 0 S, Λ spectra in jets various methods with different sensitivity to acceptance, event plane correlations, presence of additional jets, apply a correction to account for background density fluctuations 55